My reply was not repeatable!
So after some internet searching I found a car image I could use, although it wasn't a Mercedes, but what to do with it?
Craft Artist to the rescue! I found a blue paper with clouds on and another that looked like tyre marks on tarmac which I used for the background and the road. Took the car image into the programme and added a cartoon filter to it and changed the colour to blue. I was originally going to colour it with copics but changed my mind as it was so big. I did personalise the number plate but have blurred for privacy. Then for the exhaust fumes I used a speech bubble to hold the message. I printed it all out flat then printed the car and bubble again and decoupaged them. I'm pleased to say that all who signed it were impressed as was the recipient. Unfortunately just before it was given to him, someone ran into the back of the car and wrote it off! (He was OK though and apparently now has a much newer model of the car).